This invention relates generally to dynamite tubes or cartridges of the type that is used in oil field sesmic exploration and more particularly to an improved method of blow molding such plastic tubes and the improvement which results therefrom.
The improved tube has an air vent hole adjacent to or near the lower, closed portion thereof. The consistency of the dynamite used in conjunction with a cartridge is of the type that is similar to pie dough which can, and sometimes will, crumble or create air pockets as it is being packed. This hole, and its size and shape, permits the air inside the tube to be removed during the packing process.
Known prior art manufacturing techniques use a pneumatic piston and an associated needle to puncture a hole in the plastic tube. The pneumatic piston-needle combination requires more maintenance than does the present invention, arising from the requirement of an additional number of individual parts and the maintenance thereon, e.g., needle breakage, down time and labor costs in servicing of the equipment. Finally, the vent hole formed in the cartridge by known puncturing methods is irregular and often an incomplete penetration.
The vent hole of the subject invention is formed by air pressure created within the tube during the blow molding process. A unique nozzle and relay controlled valving arrangement permits the mold to effect the forming of the vent hold during the blow molding process without any "slowdown" or adverse effect on the remainder of the tube.
The present invention is directed to the above problems and, in doing do, produces a more efficient method of forming the cartridge along with an improved product as a result of the part forming method.
One object of the present invention is to eliminate entirely the need of a pneumatic hole puncher. Not only will the maintenance cost then be reduced, but also the initial production costs for the product.
Another object is to provide a unique method of forming the vent hole in a dynamite tube, wherein the use of a hole forming air pressure leaves both the interior and exterior of the cartridge smooth and snag free.
A further object of the invention is to produce a safer dynamite cartridge with lesser production costs than heretofor known. The unique manufacturing process permits the vent hole to be blown out by the air pressure (during the forming of the part) thereby forming an extent located within a recess on the outside of the tube. However, the inner tube surface remains rounded and smooth thus easily accomodating the dynamite during filling without creating "air pockets". Further, the exterior recess prevents this extent from protruding further than the side wall of the tube.
An additional object is to provide a unique method of constructing dynamite tubes with vent holes which, by the nature of the manufacturing process, will not become clogged by its own residue.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.